1. Field of the Invention
The present invention relates to an image forming apparatus employing an electrophotographic process such as a laser printer, an electrophotographic copying machine and so on.
2. Related Art Statement
A conventional image forming apparatus employing an electrophotographic process is designed so that a transferred remaining toner remained on a photosensitive body is recovered by a cleaning device, which is discharged as waste toner outside the apparatus. Since in the waste toner, often, paper powder is mixed, and characteristics outside an average particle diameter or an average quantity of charge are present, toners are abandoned without being recycled. This brings forth a rise in cleaning cost, a maintenance for replacing a waste toner box is necessary, and an environment is adversely affected.
In view of the foregoing, there has been proposed heretofore by TOSHIBA Ltd. a so-called cleanerless process in which a cleaning mechanism is not particularly provided, and where transferred remaining toner occurs on a photosensitive body, toner which is present in a non-image portion is recovered on the side of a developer carrier in a developing region during the next image preparing step for re-use for development. However, the transferred remaining toner often has a polarity reversed to the desired charge polarity under the influence of a transfer electric field or as its original properties, thus posing various problems such that the toner is not well recovered in the developing region but remained on the photosensitive body for a long period of time, resulting in filming afterward or, charging and exposing of the photosensitive body are impaired, resulting in a cause for inferior image as a memory of the previous image at the time of next image preparing step. In order to solve these problems, there are employed measures such that a memory stirring brush is provided, and a charger for arranging a desired charge polarity of a toner. However, at present, the construction becomes complicated, and the adverse influence of the transferred remaining toner cannot be removed completely, bringing forth a deterioration of image quality.
In the first place, if transfer efficiency of toner is high, a quantity of waste toner can be reduced, and even a cause for deterioration of image quality which poses a problem in a cleanerless process can be removed.
On the other hand, it is well known that by forming a toner into a spherical shape, transfer efficiency can be improved. A flowing property of toner is improved by forming a toner into a spherical shape, and a contact state between the toner and the photosensitive body comes close to a point contact, because of which adhesive force of toner with respect to the photosensitive body is reduced. However, adhesive force between a toner and a photosensitive body is reduced, and at the same time, adhesive force with an intermediate transfer body is also reduced. Therefore, a toner once transferred to the intermediate transfer body is moved at random from a position of a latent image in the vicinity of a boundary of a region to which a transfer electric field is applied and the toner becomes dust, and in a process for putting toner images of four colors one upon another on the intermediate transfer body, the toner which is already present on the intermediate transfer body is reversibly transferred to the photosensitive body at the time of thereafter transfer of toner to increase a quantity of waste toner, and further in a cleanerless process, there is a problem in that a toner is recovered in a developing device without modification to induce a mixture of colors. In a cleanerless process using a spherical toner, a procedure for improving a release property of the photosensitive body is employed in order to solve such as problem as described, but a problem such as scattering of toner cannot be basically solved unless adhesive force between the toner and the intermediate transfer body. is strengthened.
The present invention has been accomplished in view of problems as noted above with respect to prior art in an image forming apparatus employing an electrophotographic process, and has its object to provide an image forming apparatus in which a quantity of waste toner is reduced by improving transfer efficiency of toner, and it is also possible to prevent filming, a memory of images, scattering of toner, deterioration in image quality such as a mixture of colors.
For achieving the aforementioned object, the present invention provides an image forming apparatus employing an electrophotographic process in which a toner image formed on a photosensitive body is primarily transferred to an intermediate transfer body, and thereafter a secondary transfer is provided on a transfer medium, wherein surface roughness RzD1 of the photosensitive body is set to 0.01 to 10 xcexcm, and surface roughness RzD2 of the intermediate transfer body is set to 1 to 30 xcexcm, moreover being RzD1 less than RzD2.